1. Field of the Invention
The present invention relates generally to surgical implements for use in the lengthening of bones, and more specifically to an apparatus and method for intramedullary skeletal distraction.
2. Description of Related Art
The problem of limb-length discrepancies resulting from congenital, postinfectious, and post-traumatic disorders is one that has received the attention of many researchers. Various devices have been known in the art that can be attached to the ends of a sectioned bone and made to lengthen progressively, the lengthening causing growth of bone tissue at the site of sectioning and thus a commensurate lengthening of the bone. The devices are then removed when the desire length is achieved or they may be left in place as an internal splint.
External distractors, usually comprising pins passing through soft tissue and bone, can carry non-negligible potential risks of injection, pain, and muscle contractures. One benefit, however, is the accessibility of this type of device to manipulation extracutaneously.
Several internal apparatus, designed to be placed within the medulla of a long bone, have been described. Intramedullary elongation devices have also been described in prior publications.
An attempt to obviate the need for directly contacting the elongation members has been made by Grammont et al. (U.S. Pat. No. 5,074,882; Trans. 37th Ann. Mtg. Orthopaedic Research Soc., Vol. 16, p. 657, 1991). As in previous prostheses, two telescoping tubes are used to stimulate progressive elongation of a limb. A related embodiment of the device and method to be discussed herein, the disclosure of which is hereby incorporated by reference, may be found in xe2x80x9cintermedullary Skeletal Distractor and Method,xe2x80x9d U.S. Pat. No. 5,505,733, issued to D. Justin and J. D. Cole.
It is an object of the invention to provide an intramedullary skeletal distractor that elongates under the normal forces and torsions experienced in daily life and thus stimulates progressive elongation of a sectioned bone.
It is a further object of the invention to provide a device that has no extracutaneous elements.
It is another object of the invention to provide an elongation mechanism whose motion is effected with the use of a clutch and a threaded rod that together cause elongation under rotation in one direction and prevent shortening under rotation in the opposite direction.
It is an additional object to provide such a device having an elongation mechanism not subject to an axial load imposed by the patient""s weight and tissue, such as in contracture.
It is yet a further object to provide such a device that emits an extracutaneously receivable signal indicative of an amount of lengthening caused by the elongation mechanism.
These and other objects of the invention are achieved by the device and method for elongating a bone. The device, an intramedullary skeletal distractor, is responsive to rotational oscillations during normal movement within the medulla of a bone.
The present distractor is for use in a medullary cavity of a bone, and comprises a first and a second cylindrical member dimensioned such that the second cylindrical member can slide into the first in telescopic fashion. Each member has a first end, a second end, and a bore, and the members are telescoped such that the first end of the second member is positioned between the first and second ends of the first member In use, the first and second cylindrical members are attached to the proximal and distal sections of a bone, respectively.
The device further comprises an elongated rod, also having a first and a second end, with a diameter dimensioned to slide within the bore of the second cylindrical member. The first end of the rod resides within the bore of, and is affixed to, the first cylindrical member. The second end of the rod resides within the bore of the second cylindrical member.
In one embodiment clutch means are positioned within the bore of the first cylindrical member upon the elongated rod. The clutch means is selectively responsive to rotation in a first direction, upon which it operates upon the second cylindrical member to effect elongating telescopic movement. Upon rotation in the opposite second direction, the clutch means locks the rod from rotating and thus prevents contracting telescopic motion. The clutch means are positioned out of the axial (longitudinal) kinetic chain of the first and the second cylindrical members and the threaded rod, thereby preventing the clutch means from experiencing an axial load during use. This confers the advantage of permitting a finer response to rotation, as the clutch means itself need not then be sufficiently robust to withstand such an axial load.
In one subembodiment, the clutch means comprises a first and a second clutch. The first clutch is positioned in the bore of the first cylindrical member between the first ends of the first and second cylindrical members. The first clutch has an outer periphery dimensioned to fit sufficiently tightly in the bore that movement is communicated between the first cylindrical member and the first clutch. The first clutch is also positioned upon the elongated rod and is constructed so that the inner diameter of the first clutch fits sufficiently tightly thereupon that motion in the first direction is communicated thereto and that motion in the second direction permits slippage therebetween.
The second clutch is positioned within the bore of the second cylindrical member and upon a threaded portion of the elongated rod. The second clutch also has an outer periphery dimensioned to fit sufficiently tightly in the bore that movement is communicated therebetween. When rotation of the elongated rod occurs in the second direction, slippage of the elongated rod within the second clutch is permitted, and the second clutch travels along the threaded portion, pushing the second cylindrical member away from the first cylindrical member. When rotation occurs in the first direction, slippage of the elongated rod within the second clutch is not permitted, the elongated rod rotates with the second clutch, slipping within the first clutch, and no lateral motion occurs.
In an alternate embodiment, means are provided in communication with the elongated rod for determining an amount of elongation that has occurred from the starting position. This determination can be made from an extracutaneous location (i.e., noninvasively).
In another embodiment, a rotation-effecting means is provided that is affixed to the elongated rod. This means, which may take the form of a magnetically susceptible material, is responsive to an extracutaneous signal to produce rotation. Thus elongation can be effected noninvasively and controllably from a location external to the device.
The method of using the first embodiment of the skeletal distractor comprises the following steps: The device is inserted into the medulla of a bone. The first cylindrical member is then affixed to the proximal section of bone, and the second cylindrical member, to the distal section of bone. Due to the precision of the clutch mechanism used herein, during the normal motions of daily life, sufficient torsion will typically occur to activate the clutch mechanism and effect elongation. When sufficient elongation has occurred in the bone, the device is removed.
The method of using the externally driven skeletal distractor comprises the step of causing an elongating telescopic movement between the first and second cylindrical members by effecting a rotation of the elongated rod rather than depending upon physiological torsions.
The features that characterize the invention, both as to organization and method of operation, together with further objects and advantages thereof, will be better understood from the following description used in conjunction with the accompanying drawing. It is to be expressly understood that the drawing is for the purpose of illustration and description and are not intended as a definition of the limits of the invention. These and other objects attained, and advantages offered, by the present invention will become more fully apparent as the description that now follows is read in conjunction with the accompanying drawing.